1. Technical Field of the Invention
The present invention relates to a power window apparatus having a safety unit, which causes a window provided for a vehicle, such as an automobile, to be opened/closed by a motor, or the like, and performs a safety control operation for preventing pinching of the hand or the head by the window. In particular, this invention is directed to a power window apparatus having a structure with a position sensor for detecting the position of the window integrally provided with the motor.
2. Description of the Prior Art
In general, a power window apparatus incorporates a drive source, such as a motor, which causes the window to perform an opening/closing operation. With such power window apparatuses, accidents occur where a hand or a head of a person is pinched between the window glass and the sash. Therefore, an apparatus incorporating a safety unit has been suggested which interrupts the operation for closing the window or causes the window to perform an opening operation when the foregoing accident of pinching has been detected.
A power window apparatus of the foregoing type has been adapted to include a method of detecting pinching of a hand or head, or the like, by measuring the opening/closing speed of the window or the rotational speed of the motor having the correlation with the opening/closing speed. If the speed is reduced to a level lower than a reference value, that is, if loads imposed on the window and the motor are enlarged and thus the rotational speed is reduced due to a pinching action, the occurrence of the pinching is detected.
The above-mentioned detecting method, however, encounters an error in detection of pinching when movement speed of the window or rotational speed of the motor has been reduced because of contact of the window glass with a weather strip provided for the sash. As a result, the operation for closing the window is undesirably interrupted and, thus, the window cannot completely be closed. In a window incorporating a weather strip WS which has a cross sectional shape as shown in FIG. 7, and which is joined to a sash SS, the upper end of a window glass 7 starts making contact with the weather strip WS at a position about 4 mm before the fully closed position of the window. Therefore, an error in detection occurs in the region in which the foregoing contact is made. Since the above-mentioned gap of about 4 mm only allows pinching of the leading end of the finger to occur, the chances of any critical safety problems do not arise in this above-mentioned gap. Therefore, the region of 4 mm is made to be a safety-control suspension region which is not safety-controlled. In other words, the safety-control mechanism is not activated in this gap.
To recognize the safety-control suspension region, a technique has been suggested by which the position of the window is detected in accordance with an amount of rotation of the motor. However, a means for detecting an amount of rotation of the motor has a complicated structure which causes the cost to be raised. The power window apparatus has a structure that the rotational force of the motor is transmitted to the window glass through a gear mechanism, a wire and pulley mechanism and so forth. Twist occurring in the direction of rotation considered to be caused from a damper provided for the gear mechanism, elongation of the wire and abrasion of the pulley cause deviation to occur between the rotational speed of the motor and the opened/closed position of the window. As a result, recognition of the safety control region by accurately detecting the opened/closed position of the window, that is, accurate recognition of the safety-control suspension region, cannot easily be performed.
Therefore, the inventor of the present invention has suggested a power window apparatus having a structure incorporating a means for mechanically and electrically detecting the opened/closed position of the window which overcomes the above-identified problems. In such a power window apparatus, the safety-control suspension region is recognized in accordance with the detected opened/closed position of the window. As a means for mechanically and electrically detecting the opened/closed position of the window, a position sensor having a structure of a potentiometer is disposed adjacent to the closed position of the window. An output of the position sensor is used to recognize the safety-control suspension region.
However, the above-mentioned apparatus requires a space for the position sensor to be disposed adjacent to the closed position of the window. Therefore, simplification of the structure and economy of space in the vicinity of the window of an automobile cannot satisfactorily be realized. Since an error in the positioning of the sensor causes an error in detection of the opened/closed position of the window to occur, the position at which the position sensor is mounted must accurately be controlled. As a result, there arises a problem in that an operation for mounting the power window apparatus on the automobile cannot easily be completed. Another problem arises in that the accuracy to detect the position cannot easily be improved.